Abstract/Summary

This Sheet Description provides a summary of the geology
for the area of 1:50 000 Sheet 282 Devizes. The Devizes
district extends over approximately 600 km2 of north-east
Wiltshire, covering much of Salisbury Plain in the south
and most of the Vale of Pewsey in the north.
Jurassic, Cretaceous and Palaeogene strata crop out at
surface and Quaternary deposits include alluvium, peat, river
terraces and head. A full account of the stratigraphy is given
in this report, based on recent mapping and also drawing
from an extensive archive and previous publications.
Concealed strata that have been proved in deep boreholes
are also included in the description. The Oxford Clay
Formation and the Corallian Group, of Jurassic age, crop
out in the extreme north-west of the district, beyond a major
fault. The uppermost part of the Jurassic; the Kimmeridge
Clay formation, Portland and Purbeck groups, crop out
in the north-west near Devizes. However, Cretaceous
rocks underlie most of the district: the Weald Clay, Lower
Greensand, Gault and Upper Greensand formations of the
Lower Cretaceous and the Grey Chalk and White Chalk
subgroups of the Upper Cretaceous. Palaeogene strata are
rare, preserved only as a single isolated outlier capping
Sidbury Hill, near Tidworth.
T he Quaternary deposits are described in relation to
their mode of origin and they include the residual deposits,
fluvial and organic deposits, and artificial ground. A section
is devoted to applied geological issues such as geotechnical
factors that should be taken into consideration in any
land development, for example, landsliding has affected
the Upper Greensand escarpment in the north-west of the
district. The chalk is a major aquifer in the district and
an account of its hydrogeology is given. Other resources
described include sand and gravel, building stones and brick
clays. The Information Sources lists all the BGS publications
relevant to the district and gives information on how
to gain access to BGS collections and databases, including
borehole records, geophysical, geochemical and geotechnical
data.